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docs: introduce new store v3 protocol

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Hanno Cornelius 2024-02-01 17:16:48 +02:00
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@ -16,7 +16,7 @@ This specification explains the `13/WAKU2-STORE` protocol which enables querying
stored by other nodes.
It also supports pagination for more efficient querying of historical messages.
**Protocol identifier***: `/vac/waku/store/2.0.0-beta4`
**Protocol identifier***: `/vac/waku/store/3.0.0`
## Terminology
The term PII, Personally Identifiable Information,
@ -59,139 +59,260 @@ The following are not considered as part of the adversarial model:
In specific, the communication channels are assumed to be secure.
# Wire Specification
Peers communicate with each other using a request / response API.
The messages sent are Protobuf RPC messages which are implemented using [protocol buffers v3](https://developers.google.com/protocol-buffers/).
The following are the specifications of the Protobuf messages.
## Payloads
```protobuf
syntax = "proto3";
message Index {
bytes digest = 1;
sint64 receiverTime = 2;
sint64 senderTime = 3;
string pubsubTopic = 4;
// Protocol identifier: /vac/waku/store/3.0.0
package waku.store.v3;
import "waku/message/v1/message.proto";
message WakuMessageKeyValue {
optional bytes message_hash = 1; // Globally unique key for a Waku Message
optional waku.message.v1.WakuMessage message = 2; // Full message content as value
}
message PagingInfo {
uint64 pageSize = 1;
Index cursor = 2;
enum Direction {
BACKWARD = 0;
FORWARD = 1;
}
Direction direction = 3;
}
message ContentFilter {
string contentTopic = 1;
}
message HistoryQuery {
// the first field is reserved for future use
string pubsubtopic = 2;
repeated ContentFilter contentFilters = 3;
PagingInfo pagingInfo = 4;
}
message HistoryResponse {
// the first field is reserved for future use
repeated WakuMessage messages = 2;
PagingInfo pagingInfo = 3;
enum Error {
NONE = 0;
INVALID_CURSOR = 1;
}
Error error = 4;
}
message HistoryRPC {
message StoreRequest {
string request_id = 1;
HistoryQuery query = 2;
HistoryResponse response = 3;
bool return_values = 2; // Response should include full message content
// Filter criteria for content-filtered queries
optional string pubsub_topic = 10;
repeated string content_topics = 11;
optional int64 time_start = 12;
optional int64 time_end = 13;
// List of key criteria for lookup queries
repeated bytes message_hashes = 20 // Message hashes (keys) to lookup
// Pagination info. 50 Reserved
optional bytes pagination_cursor = 51; // Message hash (key) from where to start query (exclusive)
bool pagination_forward = 52;
optional uint64 pagination_limit = 53;
}
message StoreResponse {
string request_id = 1;
optional uint32 status_code = 10;
optional string status_desc = 11;
repeated WakuMessageKeyValue messages = 20;
optional bytes pagination_cursor = 51;
}
```
## General store concepts
### Index
### Waku message key-value pairs
To perform pagination,
each `WakuMessage` stored at a node running the `13/WAKU2-STORE` protocol is associated with a unique `Index` that encapsulates the following parts.
- `digest`: a sequence of bytes representing the SHA256 hash of a `WakuMessage`.
The hash is computed over the concatenation of `contentTopic` and `payload` fields of a `WakuMessage` (see [14/WAKU2-MESSAGE](/spec/14)).
- `receiverTime`: the UNIX time in nanoseconds at which the `WakuMessage` is received by the receiving node.
- `senderTime`: the UNIX time in nanoseconds at which the `WakuMessage` is generated by its sender.
- `pubsubTopic`: the pubsub topic on which the `WakuMessage` is received.
The store protocol operates as a query protocol for a key-value store of historical Waku messages,
with each entry having a [14/WAKU2-MESSAGE](https://rfc.vac.dev/spec/14/) as value
and [deterministic message hash](https://rfc.vac.dev/spec/14/#deterministic-message-hashing) as key.
The store can be queried to return either a set of keys or a set of key-value pairs.
Within the store protocol, Waku message keys and values MUST be represented in a `WakuMessageKeyValue` message.
This message MUST contain the deterministic `message_hash` as key.
It MAY contain the full `WakuMessage` as value in the `message` field,
depending on the use case as set out below.
### PagingInfo
### Waku message store eligibility
`PagingInfo` holds the information required for pagination. It consists of the following components.
- `pageSize`: A positive integer indicating the number of queried `WakuMessage`s in a `HistoryQuery`
(or retrieved `WakuMessage`s in a `HistoryResponse`).
- `cursor`: holds the `Index` of a `WakuMessage`.
- `direction`: indicates the direction of paging which can be either `FORWARD` or `BACKWARD`.
In order for a Waku message to be eligible for storage:
- it MUST be a _valid_ [14/WAKU2-MESSAGE](https://rfc.vac.dev/spec/14/).
- the `timestamp` field MUST be populated with the Unix epoch time at which the message was generated.
If at the time of storage the `timestamp` deviates by more than 20 seconds
either into the past or the future when compared to the store node’s internal clock,
the store node MAY reject the message.
- the `ephemeral` field MUST be set to `false`.
### ContentFilter
`ContentFilter` carries the information required for filtering historical messages.
- `contentTopic` represents the content topic of the queried historical `WakuMessage`.
This field maps to the `contentTopic` field of the [14/WAKU2-MESSAGE](/spec/14).
### HistoryQuery
### Waku message sorting
RPC call to query historical messages.
The key-value entries in the store MUST be time-sorted by the `WakuMessage` `timestamp` attribute.
Where two or more key-value entries have identical `timestamps`,
the entries MUST be further sorted by the natural order of their message hash keys.
Within the context of traversing over key-value entries in the store,
_"forward"_ indicates traversing the entries in ascending order,
whereas _"backward"_ indicates traversing the entries in descending order.
- The `pubsubTopic` field MUST indicate the pubsub topic of the historical messages to be retrieved.
This field denotes the pubsub topic on which `WakuMessage`s are published.
This field maps to `topicIDs` field of `Message` in [`11/WAKU2-RELAY`](/spec/11).
Leaving this field empty means no filter on the pubsub topic of message history is requested.
This field SHOULD be left empty in order to retrieve the historical `WakuMessage` regardless of the pubsub topics on which they are published.
- The `contentFilters` field MUST indicate the list of content filters based on which the historical messages are to be retrieved.
Leaving this field empty means no filter on the content topic of message history is required.
This field SHOULD be left empty in order to retrieve historical `WakuMessage` regardless of their content topics.
- `PagingInfo` holds the information required for pagination.
Its `pageSize` field indicates the number of `WakuMessage`s to be included in the corresponding `HistoryResponse`.
It is RECOMMENDED that the queried node defines a maximum page size internally.
If the querying node leaves the `pageSize` unspecified,
or if the `pageSize` exceeds the maximum page size,
the queried node SHOULD auto-paginate the `HistoryResponse` to no more than the configured maximum page size.
This allows mitigation of long response time for `HistoryQuery`.
In the forward pagination request,
the `messages` field of the `HistoryResponse` SHALL contain, at maximum,
the `pageSize` amount of `WakuMessage` whose `Index` values are larger than the given `cursor`
(and vise versa for the backward pagination).
Note that the `cursor` of a `HistoryQuery` MAY be empty (e.g., for the initial query), as such, and
depending on whether the `direction` is `BACKWARD` or `FORWARD` the last or the first `pageSize` `WakuMessage` SHALL be returned, respectively.
### Pagination
### Sorting Messages
The queried node MUST sort the `WakuMessage` based on their `Index`,
where the `senderTime` constitutes the most significant part and the `digest` comes next, and
then perform pagination on the sorted result.
As such, the retrieved page contains an ordered list of `WakuMessage` from the oldest messages to the most recent one.
Alternatively, the `receiverTime` (instead of `senderTime` ) MAY be used to sort messages during the paging process.
However, it is RECOMMENDED the use of the `senderTime` for sorting as it is invariant and
consistent across all the nodes.
This has the benefit of `cursor` reusability i.e.,
a `cursor` obtained from one node can be consistently used to query from another node.
However, this `cursor` reusability does not hold when the `receiverTime` is utilized as the receiver time is affected by the network delay and
nodes' clock asynchrony.
If a large number of entries in the store service node match the query criteria provided in a `StoreRequest`,
the client MAY make use of pagination
in a chain of store request and response transactions
to retrieve the full response in smaller batches termed _"pages"_.
Pagination can be performed either in [a _forward_ or _backward_ direction](#waku-message-sorting).
### HistoryResponse
A store client MAY indicate the maximum number of matching entries it wants in the `StoreResponse`,
by setting the page size limit in the `pagination_limit` field.
Note that a store service node MAY enforce its own limit
if the `pagination_limit` is unset
or larger than the service node's internal page size limit.
RPC call to respond to a HistoryQuery call.
- The `messages` field MUST contain the messages found,
these are [14/WAKU2-MESSAGE](/spec/14) types.
- `PagingInfo` holds the paging information based on which the querying node can resume its further history queries.
The `pageSize` indicates the number of returned Waku messages (i.e., the number of messages included in the `messages` field of `HistoryResponse`).
The `direction` is the same direction as in the corresponding `HistoryQuery`.
In the forward pagination, the `cursor` holds the `Index` of the last message in the `HistoryResponse` `messages` (and the first message in the backward paging).
Regardless of the paging direction, the retrieved `messages` are always sorted in ascending order based on their timestamp as explained in the [sorting messages](#sorting-messages) section, that is, from the oldest to the most recent.
The requester SHALL embed the returned `cursor` inside its next `HistoryQuery` to retrieve the next page of the [14/WAKU2-MESSAGE](/spec/14).
The `cursor` obtained from one node SHOULD NOT be used in a request to another node because the result may be different.
- The `error` field contains information about any error that has occurred while processing the corresponding `HistoryQuery`.
`NONE` stands for no error.
This is also the default value.
`INVALID_CURSOR` means that the `cursor` field of `HistoryQuery` does not match with the `Index` of any of the `WakuMessage` persisted by the queried node.
A `StoreResponse` with a populated `pagination_cursor` indicates that more stored entries match the query than included in the response.
A `StoreResponse` without a populated `pagination_cursor` indicates that
there are no more matching entries in the store.
The client MAY request the next page of entries from the store service node
by populating a subsequent `StoreRequest` with the `pagination_cursor` received in the `StoreResponse`. All other fields and query criteria MUST be the same as in the preceding `StoreRequest`.
A `StoreRequest` without a populated `pagination_cursor` indicates that
the client wants to retrieve the "first page" of the stored entries matching the query.
## Store Request
A client node MUST send all historical message queries within a `StoreRequest` message.
This request MUST contain a `request_id`.
The `request_id` MUST be a uniquely generated string.
If the store client requires the store service node to include Waku message values in the query response,
it MUST set `return_values` to `true`.
If the store client requires the store service node to return only message hash keys in the query response,
it SHOULD set `return_values` to `false`.
By default, therefore, the store service node assumes `return_values` to be `false`.
A store client MAY include query filter criteria in the `StoreRequest`.
There are two types of filter use cases:
1. Content filtered queries and
2. Message hash lookup queries
### Content filtered queries
A store client MAY request the store service node to filter historical entries by a content filter.
Such a client MAY create a filter on content topic, on time range or on both.
To filter on content topic, the client MUST populate _both_ the `pubsub_topic` _and_ `content_topics` field.
The client MUST NOT populate either `pubsub_topic` or `content_topics` and leave the other unset.
Both fields MUST either be set or unset.
A mixed content topic filter with just one of either `pubsub_topic` or `content_topics` set, SHOULD be regarded as an invalid request.
To filter on time range, the client MUST set `time_start`, `time_end` or both.
An unset `time_start` SHOULD be interpreted as "from the oldest stored entry".
An unset `time_end` SHOULD be interpreted as "up to the youngest stored entry".
If any of the content filter fields are set,
namely `pubsub_topic`, `content_topic`, `time_start`, or `time_end`,
the client MUST NOT set the `message_hashes` field.
### Message hash lookup queries
A store client MAY request the store service node to filter historical entries by one or more matching message hash keys.
This type of query acts as a "lookup" against a message hash key or set of keys already known to the client.
In order to perform a lookup query, the store client MUST populate the `message_hashes` field with the list of message hash keys it wants to lookup in the store service node.
If the `message_hashes` field is set,
the client MUST NOT set any of the content filter fields,
namely `pubsub_topic`, `content_topic`, `time_start`, or `time_end`.
### Presence queries
A presence query is a special type of lookup query that allows a client to check for the presence of one or more messages in the store service node,
without retrieving the full contents (values) of the messages.
This can, for example, be used as part of a reliability mechanism,
whereby store clients verify that previously published messages have been successfully stored.
In order to perform a presence query,
the store client MUST populate the `message_hashes` field in the `StoreRequest` with the list of message hashes
for which it wants to verify presence in the store service node.
The `return_values` property MUST be set to `false`.
The client SHOULD interpret every `message_hash` returned in the `messages` field of the `StoreResponse` as present in the store.
The client SHOULD assume that all other message hashes included in the original `StoreRequest` but not in the `StoreResponse` is not present in the store.
### Pagination info
The store client MAY include a message hash as `pagination_cursor`,
to indicate at which key-value entry a store service node SHOULD start the query.
The `pagination_cursor` is treated as exclusive
and the corresponding entry will not be included in subsequent store responses.
For forward queries, only messages following (see [sorting](#waku-message-sorting)) the one indexed at `pagination_cursor` will be returned.
For backward queries, only messages preceding (see [sorting](#waku-message-sorting)) the one indexed at `pagination_cursor` will be returned.
If the store client requires the store service node to perform a forward query,
it MUST set `pagination_forward` to `true`.
If the store client requires the store service node to perform a backward query,
it SHOULD set `pagination_forward` to `false`.
By default, therefore, the store service node assumes pagination to be backward.
A store client MAY indicate the maximum number of matching entries it wants in the `StoreResponse`,
by setting the page size limit in the `pagination_limit` field.
Note that a store service node MAY enforce its own limit
if the `pagination_limit` is unset
or larger than the service node's internal page size limit.
See [pagination](#pagination) for more on how the pagination info is used in store transactions.
## Store Response
In response to any `StoreRequest`,
a store service node SHOULD respond with a `StoreResponse` with a `requestId` matching that of the request.
This response MUST contain a `status_code` indicating if the request was successful or not.
Successful status codes are in the `2xx` range.
Client nodes SHOULD consider all other status codes as error codes and assume that the requested operation had failed.
In addition, the store service node MAY choose to provide a more detailed status description in the `status_desc` field.
### Filter matching
For [content filtered queries](#content-filtered-queries), an entry in the store service node matches the filter criteria in a `StoreRequest` if each of the following conditions are met:
- its `content_topic` is in the request `content_topics` set
and it was published on a matching `pubsub_topic` OR the request `content_topics` and `pubsub_topic` fields are unset
- its `timestamp` is _larger or equal_ than the request `start_time` OR the request `start_time` is unset
- its `timestamp` is _smaller_ than the request `end_time` OR the request `end_time` is unset
Note that for content filtered queries, `start_time` is treated as _inclusive_ and `end_time` is treated as _exclusive_.
For [message hash lookup queries](#message-hash-lookup-queries), an entry in the store service node matches the filter criteria if its `message_hash` is in the request `message_hashes` set.
The store service node SHOULD respond with an error code and discard the request
if the store request contains both content filter criteria and message hashes.
### Populating response messages
The store service node SHOULD populate the `messages` field in the response
only with entries matching the filter criteria provided in the corresponding request.
Regardless of whether the response is to a _forward_ or _backward_ query,
the `messages`field in the response MUST be ordered in a forward direction
according to the [message sorting rules](#waku-message-sorting).
If the corresponding `StoreRequest` has `return_values` set to true,
the service node SHOULD populate both the `message_hash` and `message` for each entry in the response.
In all other cases, the store service node SHOULD populate only the `message_hash` field for each entry in the response.
### Paginating the response
The response SHOULD NOT contain more `messages` than the `pagination_limit` provided in the corresponding `StoreRequest`.
It is RECOMMENDED that the store node defines its own maximum page size internally.
If the `pagination_limit` in the request is unset,
or exceeds this internal maximum page size,
the store service node SHOULD ignore the `pagination_limit` field and apply its own internal maximum page size.
In response to a _forward_ `StoreRequest`:
- if the `pagination_cursor` is set,
the store service node SHOULD populate the `messages` field
with matching entries following the `pagination_cursor` (exclusive).
- if the `pagination_cursor` is unset,
the store service node SHOULD populate the `messages` field
with matching entries from the first entry in the store.
- if there are still more matching entries in the store
after the maximum page size is reached while populating the response,
the store service node SHOULD populate the `pagination_cursor` in the `StoreResponse`
with the message hash key of the _last_ entry _included_ in the response.
In response to a _backward_ `StoreRequest`:
- if the `pagination_cursor` is set,
the store service node SHOULD populate the `messages` field
with matching entries preceding the `pagination_cursor` (exclusive).
- if the `pagination_cursor` is unset,
the store service node SHOULD populate the `messages` field
with matching entries from the last entry in the store.
- if there are still more matching entries in the store
after the maximum page size is reached while populating the response,
the store service node SHOULD populate the `pagination_cursor` in the `StoreResponse`
with the message hash key of the _first_ entry _included_ in the response.
# Security Consideration